Automatic control system



June 13, 11939. 1'. R. HARRISON AUTOMATIC CONTROL SYSTEM 3 Sheets-Sheet 1 Original Filed May 21, 1932 IN VEN TOR. THOMAS R. HARRISON A TTORNEY June 13, 1939.

T. R. HARRISON AUTOMATIC CONTROL SYSTEM R N 7 O Kw 8 T 0| 1 0 TR M NR EA .m u m ma 8 m M s M w. 0 R H In. T 8 3 q 7 2 Y i 1mm 8 0 9 5 mm 900000000 ank m w. I w 9 6 8 VWIF oooooooo a 2 B F ATTORNEY T. R. HARRISON 2,162,469

June 13, 1939.

AUTOIAT I C GONTRQL SYSTEM Original Filed May 21, 1932 I5 Sheets-Sheet 3 FIG] 26a REvERsmLE uoroa mmvroa THOMAS R HARRISON ATTORNEY Patented June 13, .1939

PATENT OFFlCE AUTOMATIC CONTROL SYSTEM Thomas B. Harrison. Wfl oote, PL,

assignmto.

The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania Original application May 21,-1932, Serial No. 612,735. Divided and this application August 4, 1936, Serial No. 94,143

' 11 Claims.

The present invention is a division of my prior application Serial No. 612,735, filed May 21, 1932, for Patent No. 2,058,585, granted October 27, 1936, and said prior application was a division of my application Serial No. 701,829, filed March 25, 1924, for Patent 1,898,182, granted Janua y 19, 1933. Each of the above mentioned patents discloses various improvements in automatic control systems and apparatus particularly devised for use in controlling recorders, switches, motors, valves, rheostats and like devices or instrumentalities to be controlled in response to mechanical, chemical, electrical or other physical changes of condition in order to effect a record of the changes, or to maintain predetermined physical conditions at controlled points.

The various improvements disclosed in each of the above mentioned patents were devised by me with the general objects in view, of providing simplified and more efiicient, more accurate and more rugged and reliable method and apparatus for controls and recorders, and such other objects as may be obtained by the utilization of apparatus and principle set forth in my prior application, and herein, in the many relations in which the combinations and sub-combinations claimed as novel with mi! and their equivalents, may be adapted by those skilled in theart.

The improvements claimed herein, are improvements in measuring apparatus of the potentiometric and analogous types in which a contact engaging a resistance included in a measuring circuit, is automatically adjusted along said resistance, under control of a galvanometer, as required to balance the E. M. F. of a thermocouple, or other potential to be measured, against the potential drop in a portion of the measuring circuit including more or less of said resistance.

In such measuring apparatus, it has been the practice, heretofore, to employ a power shaft rotating in one direction, and galvanometer controlled clutch means for causing that shaft to give circuit rebalancing movement in onedirection or in the opposite direction to an adjustable resistance engaging contact. The improved apparatus claimed herein, comprises a reversible electric motor controlled by the galvanometer, which by the rotation of its armature shaft in one direction or the-other, directly gives movement in one direction or the other to the resistance adjusting device. The use of a galvanometer controlled reversible motor, in lieu of a power shaft rotating in one direction and associated clutch parts, to give movement.

current recorder arrangement;

to the adjustable resistance engaging contact, simplifies the construction of the measuring apparatus, permits of more speedy rebalancing operations, and is otherwise advantageous.

Referring to the drawings: 5

Fig. 1 is a more or less diagrammatic disclosure. of the essential elements of the galva-' nometer arrangement and mechanical control, together with one form of switch circuit;

Fig. 2 is a distorted diagrammatic disclosure of the arrangement in Fig. 1 as applied to one form of recorder arrangement;

Fig. 3 shows a modified switching arrangement;

Fig. 4 shows a balancing rheostat and variable Fig. 5 shows a mechanical switch lock and release arrangement;

Fig. 6 shows a modification of the switching arrangement shown in Fig. 3;

Fig. '7 is a diagrammatic disclosure of a system in which the balancing rheostat of Fig. 4 is associated with a plurality of thermocouples and current meters.

In Fig. 1, i represents a shaft rotated at a uniform rate of speed by any suitable means, not shown, and has secured thereto an eccentric cam 2, which by its rotation rocks an arm 3 vertically about pivot 4 secured to a suitable fixed support 5. A vertical member 8 is pivoted to arm 3 at l and is urged to the right in Fig. 1 by a tension spring 8. A rojecting lug 9 is provided and forms a shoul r adapted to hook over and engage a frame 10 which in turn is pivotally mounted on a spindle H. The front edge of frame i0 is provided with inclined upper edges or surfaces I2 and 13 in a manner to form a shallow V-shaped depression therein, A

eter l5 pivoted for horizontal movement, is so arranged that the needle 16 thereof swings directly over the surfaces 12 and I! when the galvanometer is deflected and when the galvanometer is in normal position, the needle will be directly over the point of the V in the center of the frame. A pair of contact springs l1 and I l suitably supported from fixed blocks l9 and 20 are arranged above frame It in a manner not to interfere with the pivotal movement of the frame, and so that as the frame is raised so if the needle is in central position, neither of the springs will be engaged by the needle, but if the needle is deflected, atthe upper instant,

the needle will engage and force one or the other of the springs l1 and I8 causes the contacts 2| and 22 to engage adjustable contacts 23 and 24 carried in the conducting bus member 25. Formed integrally with or secured to the upper end of member 6 is an extension 26 with wings 21 and 28. A pair of hook members 29 and 30 carried by electro-magnetic switches 3| and 32 are so arranged that when the switches are actuated, and moved against the tension of springs 33 and 34, members 29 'and 30 will be moved to the left in Fig. 1; engaging wings 21 and 28 and member 6 will be moved about its pivot 1 against the tension of spring 8 until the shoulder formed by 9 is disengaged from the upper rear edge of the front end of frame In. This movement of member 6 permits frame ID to drop until arrested by stop I4. The width of wings 21 and 28 is such that the vertical movement thereof will not be sufficient to effect the release thereof, and member 6 will be held to the left in Fig. 1 as long as either switch is actuated, but will be free to move vertically under the influence of cam 2. When both switches are released and return to the position shown in Fig. 1, under the influence of springs 33 and 34, spring 8 will move member 6 to the right in Fig. 1 and as it is raised cam surface 35 will force it to the left until the shoulder formed by projection 9 is free to slide over and re-engage the upper rear edge of frame ID, as shown in Fig. 1 at approximately the upper limit of the movement of member 8.

The switches 3| and 32 may be of any well known electromagnetically actuated trip release type, which when thrown into actuated position, will remain set until released by an electromagnetic release circuit. Since such switches are supplied by well known electrical companies and are well understood in the art, more detailed disclosure will not be made. The actuating circuits for the switches 3| and 32 are controlled by contacts 2| and23, and 22 and 24 respectively, while the release circuits therefor are controlled by contacts 35' and 36. Contact 36 is carried on a spring 31 which is depressed to close the contacts by an actuating member 38 preferably of insulating material carried by member 3, when member 3 is in its lower position. The mechanism of the control instrument shown in Fig. 1 is the same as that of Fig. 2, Fig. 2 complementing Fig. 1 by showing more completely the electrical circuit.

Actuating coils 39 and 40 of switches 3| and 32 each have one terminal thereof connected by means of conductors 4| and 42 to contacts 2| and 22 respectively, and, as shown in Fig. 2, the other terminals thereof are connected to a common lead 43 through spring contact 44, insulated contact plate 45 of switch 3| in unactuated position, through conductor 46 to contact plate 41 of switch 32, to spring contact 48 in unactuated position of switch 32 to one side of a power supply line L The other side of the power supply line H is connected directly'to contacts Hand 24 through bar 25, so that when both switches are unactuated, closure of contacts 2| and 23 will complete'a circuit through coil 39 and actuate switch 3|, and closure of contacts 22 and 24 will energize coil 40 to actuate switch 32. The movement of e' .her switch will be followed for an interval by springs 44 or to maintain the energizing circuit long enough to set the switch, but before contacts 22 and 23 are moved to open their respective actuating circuits, these circuits will be interrupted at 44 and 48 respectively due to the movements of the switches 3| and 32, so that breaking of the circuits always occur at relatively heavy switch contacts 44 and 45, and 41 and 48, it being understood that contacts 45 and 41 are movable with the switches and properly insulated. In this manner destructive arcing at contacts 22 and 24 is prevented and the life thereof is considerably prolonged.

When the switches 32 and 3| reach actuated position (as shown in Fig. 2 by the dotted lines for 3|) they will engage contacts 48 and 49 respectively and be held in actuated position by means of magnetically controlled releasing trips (not shown). Contacts 48' and 49 are connected directly to L and in actuated position of the switch 3|, contact is made from contact 48' through insulated switch contact 50 through conductor 5| to trip release coil 52, through coil 52 to conductor 53 to release circuit control contact 35'. In actuated position of switch 32 contact is made from contact 49 through plate 54 thereof, through conductor 55 through coil 56 to con ductors 53 and contact 35'. When contact 36 is closed by operation of member 31, an energizing circuit is completed from L through conductor 5'1 to spring 31, contact 35', and through the release coil 52 or 56 of the actuated one of switches 3| or 32, thereby actuating the releasing trips to permit the restoration of the actuated switch to unactuated position. The conductors 58 and 59 branch from the conductors 5| and 55 respecportioned that with the rear upper edge of frame l0 engaging the shoulder formed by projection 9, the weight of members 3 and 8 and the connected parts is such as to overbalance the weight of frame H] and the galvanometer parts so that as 6 descends the front end of the frame and galvanometer needle IE will rock upward, but when cam 2 causes member 6 to move upward, the front of the frame will drop until it engages stop l4. If the galvanometer needle is in central position as it is moved upward it will pass between the ends of springs l1 and I8 and no effect on the switches will be produced. If, however, the needle is deflected it will be engaged by edge l2 or |3 depending upon whether the deflection is left or right, and as the upward movement continues, the needle will engage one or the other of the springs I"! or I8, and will close one or the other set of contacts 2| and 23, or 22 and 24, and this closure of contacts will energize coil 39 or 40 as the case may be, through the circuits above traced out, to actuate one or the other of switches 3| and 32, and thereby complete a control circuit through conductor 58 or conductor 59 as above set forth.

Actuation of either switch pulls member 6 to the left in Fig. 1-through operation of extension 29 or 30 on wings 21 or 28, so that the shoulder formed by 9 is disengaged from the upper rear edge of frame l0, and as soon as either switch is actuated, the frame is permitted to drop thereby freeing needle IE to assume a new position. It will be noted that the movement of contacts 2| and 22 may be short owing to the fact that interruption of the circuit established by these contacts always occurs at contact 44 or 48 of the switches, and in this manner the needle is free to deflect for a major portion of the time of each cycle, and is gripped only during the time rement of member 6 after ated switch, by rotation of quired to actuate the switch which is of very small duration. The weight of the parts Is relatively so small, that no injury is occasioned to the needle in event of the parts sticking or the switches failing to function. The parts will simply remain suspended while the cam drops away from member 6 without injury thereto.

The setting or actuation of either switch 6| or 32, as above set forth, partially closes a trip circuit through its release coil 52 or 56, and when member 3 approaches the lower limit of movement the contacts 65' and 66 are closed and release the actuated switch so that it may return under theinfluence of its spring to unactuated position and close the circuits for coils 66 and 66 at contacts 66 and restoration of the actucam 2, will force member 6 to the'left due to the engagement of surface 35 thereof with the rear of frame I6 until the upward limit of movement is approximately reached, at which point the shoulder formed by projection 6 will slide over and re-engage the upper rear edge of frame l6, and the cycle of operation will be complete. Member 6 and the connected parts will again move downward causing the upward movement of the front of frame I6 vlated from all of the in another cycle of operation.

Owing to the relative inclinations of edges I2 and I6, it will be clear that the point in the cycle at which the needle I6 will close the contacts 2| or 22 will vary with the amount of deflection of the needle, and the greater the deflection, the earlier in the cycle the switches 6| and 62 will be actuated. Inasmuch as the release of the switches 3| and 62 always occurs at the same point in the cycle, it will be apparent that the time during which the switches are closed will be directly determined by the amount of deflection of the .galvanometer. It will also be clear that although with the arrangement shown, the maximum time is the approximate time of one half a revolution of cam 2, this maximum time may be lengthened by causing cam 2 or another cam to close the contacts 35 and 66 at a later point in the cycle, but in sumcient time to release member 6 so that the shoulder formed by 6 may reengage the upper rear edge of frame I6 at the beginning of a cycle.

Having described a preferred form of controlling or contacting galvanometer arrangement, applications of this control to recording systems will be disclosed. In Fig. 2, the mechanism and circuits so far described, are shown with parts broken away on the upper half of the sheet.

One terminal of the galvanometer I5 is connected through conductor 66 to a conducting ring 6| of a rotary switch, and the other terminal is connected by means of conductor 62 to conducting ring 66 of the rotary switch. The line. conductor 1.? is connected directly to conducting ring 66 of the rotary switch. A plurality of thermocouples 65 located at different points, one only of which is shown, each have one terminal connected to one of the contacts 66 of the distributor or rotary switch by conductors. 61, it being understood that each contact 66 is insuother contacts and rings The other terminal of connected by means of traveling contactor 66 of on the distributor face. each thermocouple is conductors 66 to the a recorder individual preferably of a type similar to the Westinghouse type M graphic meter or like instrument, and

66. The upward move-.

that the switches remain closed thereto. This recorder is in general may comprise a traveling member 16 upon which 66 is mounted, and which in turn travels upon a screw threaded shaft 1| which is driven through gears 12 and 16 from a reversing motor 16. Traveling member 16 carries a pen 15 which traces a record 16 on record 'sheet 11, as determined by the movement of the sheet and the movements of the pen. The slider 66 travels over a resistance slide wire 16 of a potentiometer arrangement which comprises the battery 16, the fixed resistance 66, and the adjustable or compensating resistance 6| all connected in series. The potentlometers are each connected to a separate and insulated contact 62 of the distributor by conductor 63. One terminal of each motor reversing circuit is connected by conductors 66' to a separate and insulated contact 66 of the distributor, and the other terminals of the motor reversing circuits are connected by conductors 66 and 61 at common points A and B, to the leads 56 and 56 from switches II and 62 respectively. Distributor brush arm 66, mounted on shaft 66, is provided with brushes 66, 6|, and 62 insulated from the arm and from each other. Brush 66 connects contacts 66 to ring 6|, brush 6| connects contacts 62 to ring 66, and brush 62- connects contacts 66 to ring 66. Shaft 66 is rotated in the usual manner at a uniform speed, or by special means hereinafter described, and connects each thermocouple and its individual recorder successively to the contacting common galvanometer and common switches 3| and 62.

As a potentiometer is utilized for each recorder, it becomes desirable to periodically adjust the potentiometersagainst a standard cell. This adjustment may be effected manually if desired, but is preferably effected automatically. For automatic adjustment, a pair of rotary distributor switches with contacts 66 and 65, and brushes 66 and 61 are provided. Brushes 66 and 61 are carried on shaft 66, or rotated otherwise in definite timed relation with respect to arm 66. The contacts 66 and 65 are connected to the ends of the potentiometer resistances 66 by conductors 66 and 66. Brush 66 is connected through a standard cell I66 to a common point C, and arm 61 is connected by conductor I62 to a common point D. Point C is connected by conductors I63 to a separate distributor contact 62 for each potentiometer to be adjusted, and point D is connected by separate conductors I66 to separate distributor contacts 66, one for each potentiometer to be adjusted. It will be understood that the set of contacts for the potentiometer adjustments and the set for the individual recorder circuits may be chosen in any two sectors of the distributor and are spaced apart for convenient illustration, but in practice it will be preferable to adjust the potentiometer just before the recorder individual thereto is connected to the common galvanometer and switches. Contact 66 of the potentiometer may be connected to the lead 66' of a separate reversible motor similar to motor 16 which separate motor drives shaft I65, pinion I66, gear I61, and screw shaft I 66. Upon shaft I66 a traveling member I66 is carried to which is secured an adjusting slider 6 arranged to short cir cuit part of the resistance 6| through conductor III. The leads 66 and 61 of this potentiometer current standardizing motor will be connected to points A and B respectively. If desired where only one recorder is provided, or a standard cell is utilized with each potentiometer the recorder motor 16 may be utilized to drive shaft I66. by

providing a cam. actuated clutch driven from shaft 89 to throw shafts II and I08 in and out of driving relation with respect to the motor II at the proper times, so that when the brushes.

to control switches 3| and 33 has already been described. Assuming brush arm 88 to beon the sector for the recorder shown in this position brushes 96 and 9'! will be off contacts 94 and 95. If the position of slider 69 is such that the potential drop of the left hand section in Fig. 2 differs from the potential generated by the thermocouple, which potentials are always opposed, a current will flow through the couple, conductor 61,

. contact 86, brush 90, ring 6|, conductor 50, galvanometer I5,-conductor 62, ring 63, brush 9!, contact 82, conductor 83 left of slide wire 18, member 69, and conductor 68 to the couple. According to the direction of this current, needle IE will deflect right or left, and will actuate switch 32 or 3|, accordingly, closing a circuit to the forward or reverse circuit or motor I4 through leads 58 or 59. This circuit will remain closed until contacts 35' and 36 are closed to open the actuated switch. While the switches 3| or 32 are closed, motor M will be rotated in the proper direction to restore the balance in the galvanometer circuit by adjusting the length of wire I8 in this circuit. As soon as the switch 3| or 32 is opened, the motor I4 stops. Shaft 89 is driven in properly timed relation with respect to cam shaft I so that one or more complete cycles of the contacting galvanometer occur during the interval that brushes 90, 9|, and 92 remain in the sector. As member I shifts to balance the galvanometer coil, pen I5 is moved and traces a record of the change in conditions on sheet 11. The movement of arm 38 connects successive recorders in properly timed relation to the galvanometer circuit and switches controlled thereby.

At the proper time the arm 08 connects the potentiometer adjusting means in the circuit and at this time arms 96 and 91 will be on the proper contacts 04 and 95. In this position the potential drop across resistance 80 due to battery I9, and the potential due to the standard cell are opposed in the galvanometer circuit. If these potentials are unbalanced the galvanometer will be deflected and as at this time the other reversible motor I4 (not shown) driving shaft I05 is in the circuit closed by switch 3| or 32, slider I I0 will be shifted in a direction to restore the balance of the galvanometer and will accordingly re-establish a standard condition in the potentiometer circuit.

To provide for establishing a complete balance in each circuitbefore the switches are shifted to the next set of contacts to connect in a new recorder or potentiometer set, a modification is shown in Fig. 3. Fastened to member 6 is a projecting spring contact member H2, and fastened to a fixed supportis a co-acting spring contact member II3. Contacts 2 and 3 control a circuit through conductors I I4 and H5, a source of electricity II 6 and a stepping magnet III. Magnet I I1 actuates an armature II 8 to which a stepping pawl IE9 is pivoted. Pawl IIS is forced of contacts.

against ratchet wheel I20 by a spring I2 I. Wheel I20 is rigidly secured to and drives shaft 89 and a jockey roller I22 on a spring I23, or other suitable device is provided to properly position the distributor shaft-at each step. Each actuation of magnet III will advance the switch one step, from one contact sector to the next. Contacts H2 and H3 are so positioned that so long as the galvanometer is deflected and actuates either contact 2| or 22, theywill not engage as the movement of member 6 to the left when switches 3| or 32 close pulls contact I I2 clear of contact II3. As soon as the needle I6 reaches central position, however, neither switch 3| nor 32 will be actuated and in the downward movement of 6, contact I I2 will engage contact 3 and actuate magnet I II to advance the arm 88 to the next set It will be apparent that each recorder or controlled circuit will be brought to a balance in this manner, before the galvanometer and switches 36 and 32 are connected to the next controlling circuit.

By suitable mechanisms the stepping of the ratchet wheel I20 may be carried out in equivalent mechanical manner. As shown in Figs. 6, for example, the lever 8 may have its fulcrum pivot I I8 between its ends and be so located that it will be engaged by the part II 2 and oscillated to advance the wheel I20 one step, when the member 6 is lowered while in engagement with the frame III. In Fig. 6, the part II2 serves no electric contact purpose, but merely as a hook or shoulder for engaging and oscillating the lever I I8. When the member 6 is tilted out of the position in which the shoulder 9 engages the frame I0, the part 2 of Fig. 6 can move down past the lever II8 without engaging the latter.

In Fig. 4, an arrangement for utilizing a balancing rheostat arrangement and a variable current recorder to replace the potentiometer rccorders disclosed in Fig. 2 is provided. In this arrangement the leads 6'! and 83 from contacts 66 and 82 are connected across a fixed resistance I24. A resistance I25 is substituted for slide wire I8 in Fig. 2 across which slider 69 carried by member I0 will move. Between resistances I24 and I25 a variable current recording meter I 26 of any well known type is connected in series. A fixed resistance I2! is connected at one end to resistance I24 and at the other end is connected to resistance I 25. Connected to the junction of resistances I 24 and I2! is a resistance I28, which at its other end is connected to a resistance I29, in turn connected to the junction of resistance I25 and the recording meter. Connected from the junction of resistances I28 and I20 to the slider 63 by conductor I30 is a cell I3| which need not be standard, nor compensated against a standard cell as in the potentiometer arrangement. Leads 86 and 81 go to points A and B and laead 83' goes to other proper distributor contact In operation a current normally flows through from the cell |3I through I30, slider 69, the left end of resistance I25, through recording meter I26, resistance I24, resistance I28 to the cell I3I. The potential drop across resistance I24 will be balanced against the potential generated by the couple and'when these potentials are unequal the galvanometer will be deflected and set the motor I4 in motion in the proper direction to reestablish the balance in the galvanometer circuit by shifting the slider to vary the current flowing through the recorder and resistance I24. In this manner, independently of potential variatact 6| to the particular contact circuits connected to tions in the cell III, the current maintained through resistance I24 is always directly proportional to the potential generated by the thermocouple when a balance is effected in the galvanometer circuit, and the current flowing through the recorder I26 will produce an accurate record of the changes in the couple. The flow of current through the right section of resistance I25 and through I21 takes care of the superfluous electrical energy, and it is only necessary that cell I3I be at all times large enough to maintain sui'licient current flowing through resistance I24.

In the arrangement described for Fig. 4, a

balancing rheostat arrangement and reversing motor is'provided for each meter. It will, however, be apparent that by introducing suitable switching arrangements, a single balancing rheostat and'reversing motor may be made common to the various recorder and thermocouple circuits.

One such suitable switching arrangement may be formed, for example, by making such changes in the circuit connections to the galvanometer controlled rotary switch or distributor of Fig. 2, that said switch will successively connect each of the diiferent thermocouples in series with the galvanometer and resistance I24, and will connect each of the different meters to the balancing rheostat when the corresponding thermocouple is connected to the galvanometer and resistance I24.

One form of the switching arrangement last referred to is illustrated in Fig. '7, wherein 65A, 65B, 65C, and 65D, represent the thermocouples, and I26A, I263, I260 and I26D the current meters which may pertain, respectively, to four different furnaces, the latter not being shown. In Fig. 'l, the lower end of the rheostat resistance I24 is permanently connected to one terminal of each thermocouple by a conductor 660, and is permanently connected to one terminal of each meter by a conductor I26E. The other terminals of the difl'erent thermocouples 65A, 65B, 65C and 65D are connected to the corresponding switch contacts 66 by conductors 61A, 61B, 61C, and 61D, respectively. The second terminals of the different meters I26A, I26B, I26C,- and I26D are connected to the corresponding switch contacts 62 by conductors I26a, I26b, i260, and I26d, respectively. One galvanometer coil is connected by conductor 66 to the switch contact 6i, and the other galvanometer coil terminal is permanently connected by conductor 62 to the common point of rheostat resistances I24, I21, and I26. The switch contact 63 is permanently connected to the common point of the rheostat resistances I25 and I29 by a conductor I260. The galvanometer control circuit conductors 56 and 53 are connected directly to the corresponding reversing terminals of the reversible rheostat motor I4, and the third terminal of the motor is directly connected by conductor 63' to the supply circuit conductor L. The galvanometer of Fig. 7 may be constructed, and may have its contacts. and control the supply conductors L and L, as illustrated in Figs. 1 and 2. In Fig. I the rotary switch contacts 64, 64. and 62 of Fig. 2 are not needed and are not shown.

In the position of the switch arm 66 shown in Fig. '1, the movable contact 66 connects the con- 66 connected to the conductor 61A, and the movable contact 9| connects the contact 63 to the particular contact 62, to which the conductor I26a is connected.

In such position of the switch arm, the thermocouple 65A is operatively connected to the galvanometer and balancing rheostat and the current nmter I26A is operatively connected to the meters, and the remaining thermocouples and rheostats are open circuited. When the shaft 69 and switch arm are angularly advanced counter-clockwise one-quarter of a turn, thermocoupleIiSA and meter I26A are open circuited, and thermocouple 65B and meter I26B are operatively connected to the galvanometer and rheostat. The two following quarter turns of the switch arm 66 bring into operative relation with the galvanometer and rheostat, first the thermocouple 65C and meter I26C, and then the thermocouple 65D and meter I26D. The next quarter turn of the arm 68 will restore the conditions shown in Fig. 7.

The releasing coils 52 and 56 of switches and 32, together with contacts 35 and 36 may be eliminated and a mechanical catch arrangement substituted therefor, as shown in Fig. 5. In this event a cam projection I32 is secured to the member 6 and is arranged to engage a cam projection I33 carried by aflat spring I34. The springs 33 and 34 of switches 3| and 32 are eliminated in this form. When either of these switches is actuated member 6 will. be forced to the left, forcing member I33 and spring I34 upward until member I34 can snap over I33 and lock member 6 to the left. As the member 6 approaches the limit of its downward movement, member I32 will drop below I33, and spring 6 will then move 6 to the right, in this manner opening the actuated switch. The switches may also be actuated mechanically instead of electrically by interposing mechanical controlling elements between constantly reciprocating cam actuated members through the functioning of the needle I6, frame III, and mechanical members to replace contacts 2I and 22.

Having described preferred embodiments of the invention, of which many modifications may be made within the sprit thereof by those skilled in the art, what is desired to be secured by Letters Patent and claimed as new is:

1. In a self-balancing measuring instrument, the combination with measuring circuit means including a resistor and a contact engaging said terminal of the resistor, said contact and resistor being relatively adjustable to vary the point along the length of said resistor at which the latter is engaged by the contact, a reversible rotatable electric motor adapted to relatively adjust said contact and resistor to thereby adjust the point of their engagement along the length of said resistor in one direction or the other accordingly as the motor is rotated in one direction or the other, a -device adapted to be connected to said circuit andto a source of variable electromotive force for actuation in a direction and to an extent selectively dependent on the direction and extent of change in said force, and periodically operating control means through which said device periodically energizes said motor for operation in a direction and for a period of time selectively dependent on the direction and extent of the then current actuation of said device.

2. In a self-balancing instrument, the combination with a measuring circuit adapted for connection to a source of variable electromotive force and to be unbalanced by a variation in said force and including a resistor and a contact engaging said resistor and adjustable along its length to rebalance the circuit when the latteris unbalanced. a reversibly rotatable electric motor adapted when rotated to adjust said contact along said resistor in a direction and to an extent dependent on the direction and extent of rotation of the motor, a device responsive to unbalance in said circuit and including a pointer deflecting away from a neutral position in a direction and to an extent dependent upon the direction and extent of said unbalance, and means controlling the operation of said motor including two relatively movable parts at the same side of the path of deflection of said pointer but at opposite sides of the neutral pointer position and a cooperating member at the opposite side of the path of deflection, periodically operating means for eifecting an approach movement and a following separation movement of each of said parts and member in a direction transverse to said path once during each of regularly recurring operation periods, said member and each of said parts having pointer engaging surfaces relatively shaped for clamping engagement with said pointer, when the latter is deflected to the corresponding side of neutral, at the end of a fraction of each operating period in predetermined correspondence with the extent of pointer deflection from neutral, and means actuated by the engagement of said member and either of said parts with the pointer for operating said motor in a direction selectively dependent on the direction of pointer deflection from neutral and for a period varying in magnitude in predetermined accordance with the extent of said deflection.

3. In a self-balancing measuring instrument, the combination with measuring circuit means including a resistor and a contact engaging said resistor, said contact and resistor being relatively adjustable to vary the point along the length of said resistor at which the latter is engaged by the contact, a reversible rotatable electric motor adapted to relatively adjust said contact and resistor to thereby adjust the point of their engagement along the length of said resistor in one direction or the other accordingly as the motor is rotated in one direction or the other, a device adapted to be connected to said circuit and to a source of variable electromotive force to respond to changes in said electromotive force, and adapted to be actuated on each such response in a direction and to an extent selectively dependent on the direction and extent of the corresponding change in said force, and control means through which said device is adapted on each said actuation to energize said motor for operation in a direction and to an extent selectively dependent upon the direction and extent of said actuation.

4. In a self-balancing measuring instrument, the combination with measuring circuit means including a. resistor and a contact engaging said resistor, said contact and resistor being relatively adjustable to vary the point along the length of said resistor at which the latter is engaged by the contact, a reversible rotatable electric motor adapted to relatively adjust said contact and resistor to thereby adjust the point of their engagement along the length of said resistor in one direction or the other accordingly as the motor is rotated in one direction or the other, a. galvanometer having a definite deflection range and adapted to be connected to said circuit means and to a source of variable electromotive force for deflection in selective accordance with the direction of a change in said electromotive force and adapted on each such deflection to pass from any deflective position in said range occupied when said change is initiated to a second deflective position in said range separated from the first mentioned position by a distance corresponding to the magnitude of said change, and means controlled by the deflection of the galvanometer to one side or the other of a predetermined intermediate position for energizing said motor for rotation in one direction or the other, dependent onthe side of said intermediate position to which said galvanometer deflects.

5. A self-balancing instrument combination as specified in claim 3, adapted to respond successively to the electromotive forces of a plurality of sources of variable electromotive force and comprising a selector switch adapted to eifect the connection and disconnection of said circuit successively with the different sources, electrical relay means controlling the operation of said selector switch, and means responsive to a balanced condition of said circuitto control said relay means.

6. A self-balancing instrument combination as specified in claim 3, including means whereby on each energization of said reversible motor, the latter operates for a period of time depending on the extent of actuation of said device.

7. In a self-balancing measuring instrument, the combination with measuring circuit means including a. resistor and a contact engaging said resistor, said contact and resistor being relatively adjustable to vary the point along the length of said resistor at which the latter is engaged by the contact, a reversibly rotatable electric motor adapted to relatively adjust said contact and resistor and thereby adjust the point of their engagement along the length of said resistor in one direction or the other accordingly as the motor is rotated in one direction or the other, a galvanometer including a pointer and adapted to be connected to said circuit means and to a source of variable electromotive force, for deflection of said pointer about an axis in one direction or the other on an increase or decrease, respectively, in said force, and free whenever deflecting toward a normal, neutral pointer position from a position at either side thereof to deflect to the other side of said neutral position, and means tending to maintain said pointer in said neutral position comprising motor controlling means controlled by the deflection of said pointer for energizing said motor for rotation in one direction or the other dependent on the direction of said deflection.

8. An instrument as specified in claim 7, in

which the motor controlling means comprises a device pivoted on an axis extending transversely of the pointer deflection axis and provided with graduated galvanometer pointer engaging surfaces arranged on opposite sides of the neutral pointer position, cam means for periodically oscillating said device into a position in which one or another of said surfaces engages said pointer when the latter is deflected from its neutral position, and electrical contacts for controlling said motor and arranged to be actuated at a point in the oscillation period of said device, depending upon the deflective position of said pointer when contacted by said device, and thereby energizing said motor for a period, depending upon said deflective position.

9. In potentiometric apparatus for measuring the variable electromotive force of a source of said force and comprising automatic recalibrating means, the combination of potentiometric measuring circuit means including a variable measuring resistance, a variable calibrating resistance and a circuit energizing battery, a stand CHEM 10. In a self-balancing potentiometric measuringt torthevariahle'eleotromotiveiorceoiaamirce'oisakltoreethecunnimation of potentiometric [measuring circuit means comprising an elongated resistance, a galvanolneter adapted to deflect about an axis. means includin a contact movably engagin said resistance for connecting said galvanometer and correlate said circuit means, a guidewa! alongsidesaid resistance, a carriage carrying said contactandmovabiealongsfldguidewaytothcrelfl varythepointalongtheiengthoftherulstanoe' atwhichtheiatterisengagedhysaidcontact.

gives movementto saidcan'iagealongsaidnndewayinonedirectionortheothenandcontrolling 7 mrunummmoma am- 'lyoacilatlnacam-actnateddeviceandeiectriul km in! controlled by the deflection d I .md'mcnumotedmm- 'atefldmtm'atapdntintheoecillaflngperlod otsaiddericadexiendinguponthedeflectionotaaid.

-11. Ina aelt-halandng potentiomeh'lo measurimimmlenttormeaanrimthewarlableeleeloaned amid nidtotoetln at cwiticmetrl dmalt ne'anlcumdlnganeimmatedmisiama-galadapted nonmetal tni'biicct-ainmtanaaia. mansinclndingacimtactmovahlysaid reistanoeforsaid and aouroetosaidclrcuitmeam'aguidemalongsidesaidresistamacarriagemrryingsaidcom tact and movable long said guidem to thereby vary the point along the length at the resistance at'hichtheiatterisbysaidoontwta reversible rotating motor, a drive connection hetieensaidmotorandcarriagawhenewrotation otthelnotorinonedireotionortheothergim movement to said carriage along said guideway in one direction or the other, controlling means (or I said motor which includes a periodically oscillating cam-actuated device and electrical contact devices controlled by the deflection of said galvanometer, and which is adapted to actuate said nmtoratapointintheoecillatingperiodoisaid device, depending upon the existing deflection of said galvanorneter. a marker carried bysaid cartinge. and means for supporting and advancing a record chart with a portion thereof alongside said guideway in position for engagement by said marker.

THOMAS E. HARRISON.

cam-mars or com moi or the above patent requiring v moms R'. It ieherehy certified that error appears in the printed June 13 1939 HARRISON.

specification correction as follows: Page 2, seccicpilizmn, lines 22 and 23, for 'ccnidnctor Sjthrough coil 56 to conductors 53" read conductors 55 coil 56to conductor 53; page 5, second 'col- 7mm, line 1 for the "meters" read rheostat; line 5, for-"rheoet ate read meters; page 7, prising .cla'in 11; and that the correction therein that the same the Patent urnc.

second 'colum', strike out lines 8 to 36 inclusive canam Letters Patent should be read with this my conformto the record of. the case in Signed and sealed an 5:1; as", of September, a, n. -19 9'.

- (S al) Henry Van Arsdale, Acting Comissioner ot Patents. 

